How do we know that abiding in Christ is necessary for Christians?

In John 15:4-5, Jesus articulates the necessity of abiding in Him, stating, 'As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me.' This passage emphasizes that spiritual vitality and fruitfulness are directly dependent on one's relationship with Christ. Abiding in Christ involves a continuous reliance on His life-giving grace and a commitment to Him as Lord. Apart from this abiding relationship, any attempts at producing fruit are in vain, echoing the theme of total dependence on God's grace. This is a core principle in Reformed theology, which teaches that salvation and sanctification are found solely in the sufficiency of Christ and are applied to believers by faith.